1. Field of the Invention
The present invention generally relates to a method of and an apparatus for recording information on a record medium such as an optical disc, and an apparatus for reproducing the information from the record medium, and more particularly, to an improvement in the access time as for the information recording and reproducing apparatuses.
2. Description of the Related Art
Along with the recent development in the multi-media technique, the high density recording of video and audio information is frequently performed. The high efficiency encoding process of the video and audio information has been developed as a technique to record as much information as possible onto the record medium having a limited record capacity. Especially, the method proposed by the MPEG (Motion Picture Experts Group) that is an international standardization meeting for accumulation medium animation image encoding (hereafter, referred to as an MPEG method) is noted as a standard for the compression method by means of high efficiency encoding of the video information.
In the consecutive frame pictures, the pictures ahead of and behind each other are generally similar to each other. The MPEG method is a method of noting this point and generating, on the basis of a plurality of frame pictures transferred at an interval of a few frames, a different frame picture existing between the pertinent plurality of frame pictures, by means of an interpolation operation based on a moving vector of an original picture and the like.
In this case, in a case of recording the different frame pictures, only by recording information with respect to a difference between the plurality of frame pictures and the moving vector, at a time of reproducing, it is possible to refer to them, predict from the above mentioned plurality of frame pictures and thereby reproduce the appropriate different frame pictures. As a result, it is possible to carry out the compression record of the video data.
Here, in the MPEG method, a unit of GOP (Group of Picture) is used, as a minimum unit which enables a reproduction without referring to other pictures. FIG. 7 shows a bit stream in such a high efficiency encoding process constituting this one GOP. Each frame indicates one frame picture. In FIG. 7, one GOP is composed of twelve sheets of frame pictures. However, in the frame pictures, a frame picture illustrated by a sign (I) is referred to as an I picture (Intra-coded picture), and it means the frame picture which can be reproduced as a perfect frame picture from the picture itself. And, a frame picture illustrated by a sign (P) is referred to as a P picture (Predictive-coded picture), and it is a predictive picture generated by decoding a difference from the predictive pictures which are compensation-reproduced on the basis of a demodulated I picture or other P pictures. And, a frame picture illustrated by a sign (B) is referred to as a B picture (Bidirectionally predictive-coded picture), and it means a predictive picture reproduced by using not only the demodulated I picture or P picture but also a future I picture or P picture recorded on an optical disk and the like to predict. FIG. 7 shows a predictive relation (interpolation relation) between respective pictures by using an arrow mark.
Here, as to data generation amount of one GOP, there are two different generation ways. FIG. 8A shows the GOP recorded by controlling a compression rate and the like such that the data generation amount (n, n, n) for each GOP 100 is always constant. If the data generation amount is constant, an address of each GOP and the data amount have proportional relation between each other. Thus, it is possible to easily search the appropriate address corresponding to a target time. On the other hand, FIG. 8B shows the GOP generated without controlling so as to make the data generation amount constant (a, b, c). At this time, in respective recorded GOPs 101, 102 and 103, the data amounts included therein become different from each other.
Now, noting the data amount generated in a case that recorded video information is reproduced, the picture in which movement of an original picture is large has slightly relative relation between respective pictures, so that the data amount generated in one GOP becomes large. On the other hand, the picture in which the movement of the original picture is slight has largely relative relation between the respective pictures, so that the data amount generated in one GOP becomes small. According to the method shown in FIG. 8A, each GOP is adapted to have always constant data amount irrespective of a content of a moving component of the original picture. Thus, image quality is made worse for the video picture whose movement is large, and uselessness is induced in the video picture whose movement is small. As a result, the method shown in FIG. 8B is desired in order to make the image quality uniform and to effectively utilize a record capacity of the optical disk. It is concluded that it is appropriate to differentiate the data amount for each information unit such as the GOP, in the information recording method by means of the ordinary high efficiency encoding process.
Next, as shown in FIG. 9, when recording on the optical disk the video information compressed, together with audio information to which a predetermined process such as a compression and the like is applied, the compressed video information is time-axis-divided and multiplexed into one data stream. And, the video information and the audio information which are time-division-multiplexed are recorded with a packet data as a unit.
In the multiplexed stream data recorded in this way, as shown in FIG. 10, for the sake of convenience of the access at a time of reproducing, time-axis information is added for every packet. In the MPEG method, this time-axis information is referred to as PTS (Presentation Time Stamp). In the PTS, a reproduction time of the video information or the audio information with respect each of the packets is described with 1/90000 sec as one unit (that is, 90000 Hz). At a time of multiplexing the video information and the audio information to record, as shown in FIG. 10, the same PTSs are described and recorded on the corresponding video packet and audio packet. Thus, the reproducing apparatus refers to the PTSs and causes the packet of the video information and the packet of the audio information, in which the same PTSs are recorded on both packets, to be synchronized with each other, and thereby can reproduce the video information and the audio information by causing them to be synchronized with each other.
On the other hand, the PTS can be used as elapsed time information at a time of reproducing. That is, by storing the PTS obtained from the optical disk at a time of starting the reproduction, by obtaining a difference between the PTS detected in a middle of the reproduction and the PTS at the time of starting the reproduction, and by dividing the difference by 90000 (=90 kHz), it is possible to obtain the elapsed time from the beginning of the reproduction.
However, in case of the recording method of FIG. 8B in which the data amounts are different in each GOP, there is a problem that it takes a relatively long time until the reproducing apparatus starts reproducing the target information since the arbitrary time to specify the target information is specified to the reproducing apparatus. Hereinbelow, this problem will be explained in more detail.
In the above mentioned information reproducing apparatus, when the target time is given to it, it refers to the time axis information e.g. the PTS, and then accesses the information according to a predetermined procedure.
Namely:
i) it accesses the lead address of the record medium; PA1 ii) it judges the approximate position from the specified target time, and slides the optical pickup device to the approximate position; PA1 iii) it reproduces the information from the position to which the optical pickup has been slid, and detects the PTS thereat; and PA1 iv) it calculates the elapsed time from the detected PTS, judges the approximate position again from the difference between the calculated elapsed time and the target time, and slides the optical pickup device again to the approximate position; and PA1 v) it repeats the above processes i) to iv) until it accomplishes a convergence at the target position.
That is why it takes a certainly long time to accomplish the convergence.
There are some methods to reduce the access time.
For example, there is a method of dividing the software to be recorded onto the record medium into a certain number of chapters depending on the content of the software, and recording the lead address of each chapter at a predetermined portion on the record medium. According to this method, the compressed and multiplexed video information and the multiplexed audio information are recorded in the video and audio information area in FIG. 11A, while the lead address of each chapter is recorded in the access information area, which is located at the inner circumference side of the record medium, in FIG. 11A. Here, by dividing the compressed information by each block (corresponding to the chapter) of 2048 bytes, the serial number from the lead of each block may be assigned to the address for each block, for example. The access information based on this method is shown in FIG. 11B.
Further, other than the above mentioned methods, there is a method of calculating the data amount for each GOP in a recording apparatus, and recording all of the lead addresses of GOPs to the access information area. The access information based on this method is shown in FIG. 11C.
However, according to the method by use of the access information of FIG. 11B, the access time can be reduced by the time period corresponding to the lead address of each chapter. Namely, in order to access the address corresponding to the target time specified arbitrarily, the aforementioned processes i) to iv) should be performed.
On the other hand, according to the method by use of the access information of FIG. 11C, if the number of frames constituting the GOP is changed in the middle of the record medium, the elapsed time for each start address is also changed, resulting in that it is difficult to search the address precisely when the target time is specified.